A double blind randomised placebo controlled parallel trial of the effect of fosinopril, an angiotensin converting enzyme inhibitor, on the quadriceps muscle in 80 COPD patients who have quadriceps weakness. Patients will have a baseline assessment including measures of quadriceps strength and endurance and a quadriceps biopsy. Patients with weakness will be randomised to ACE inhibitor or placebo and re-assessed after three months of treatment.